Tuberculosis (TB) remains a top ten cause of death globally, partly due to its prolonged treatment time, currently comprised of several drugs for 6-12 months (1). The discovery of novel strategies to decrease treatment time is thus paramount to global TB management. One emerging strategy is the inhibition of two-component regulatory systems of Mycobacterium tuberculosis, the etiological agent of TB (2). In this study, we characterise a two-component system (TCS) of M. tuberculosis, TcrXY, comprised of the sensor kinase TcrY and response regulator TcrX, and demonstrate its potential as a therapeutic target for TB.
We demonstrate that TcrXY is an acid-sensing TCS of M. tuberculosis that is important for adaptation to environments encountered in the macrophage phagosome, the primary niche of M. tuberculosis in the host. The tcrXY operon is strongly induced transcriptionally in M. tuberculosis during acid stress in vitro and during the infection of cultured macrophages. Using transcriptomics, we provide the first description of the TcrXY regulon, comprised of approximately 60 acid-regulated genes. One notable regulon member is a putative protein/peptide translocation system that is expressed during macrophage infection in a TcrXY-dependent manner.
We investigated the role of TcrXY in virulence and the potential of TcrXY targeting to improve treatment efficiency in a murine model of TB. A doxycycline-inducible CRISPR-dCas9 based gene silencing system was employed to knockdown tcrX expression in virulent M. tuberculosis, H37Rv (3). Transcriptional silencing of tcrX significantly attenuated the persistence of H37Rv in the lungs and spleens of infected mice. Alongside treatment with rifampicin and isoniazid, the knockdown of tcrX resulted in a statistically significant 1-log reduction in mycobacterial burden in the lungs of infected mice, as compared to mice in which tcrX remained active.
In this work, we have identified, characterised, and validated, an attractive inhibitory target to improve the treatment of TB and potentially shorten therapy duration. Our efforts are now invested toward the discovery of novel small molecule inhibitors of the TcrXY system.